Latently infected CD4+ T cells represent the major barrier to HIV-1 eradication. Many strategies are being developed to eliminate these cells, but the field lacks a simple sensitive assay that can screen for these cells. PCR based assays cannot distinguish between replication-competent versus defective virus and recent studies have shown that the current state of the art culture assay measures only a small fraction of the replication-competent virus present. In this proposal we aim to develop a sensitive assay that is capable of selectively amplifying replication-competent virus from latently infected CD4+ T cells. Such an assay could inform the decision of whether or not to discontinue cART in patients after a therapeutic intervention is made. The need for such an assay is highlighted by the recent report of the 2 Boston patients who were treated with allogeneic stem cell transplantation for malignancies. No HIV DNA was detected by PCR in either patient from as many as 200 million PBMCs (<0.07 copies/106 PBMCs), but after cART was discontinued there was a rapid rebound in viremia in both patients. This outcome is undesirable is it negates the theoretical advantages to having smaller HIV-1 reservoirs. The development of a simple but sensitive assay that can screen a very large number of CD4+ T cells may help prevent the occurrence of a similar scenario from occurring in the future. This work will be important for the development of strategies for HIV-1 eradication since the assay will help inform the decision of whether or not to discontinue antiretroviral therapy.